1. Field of the Invention
This invention relates to medical devices. Specifically, but not by way of limitation, this invention relates to inserting a micro-catheter such as an electrode into a patient.
2. Background
In this document, any medical device that acts on the tissue of the patient is classified as a primary medical device. Other medical devices that assist in the positioning or handling or operation of the primary medical device are called secondary medical devices. While the secondary medical device could be used to introduce a primary medical device to several locations within a patient, for the discussion in this document, a neurosurgical procedure will be used as an example.
A common surgical technique inserts primary medical devices into patients through small openings that are surgically cut in the patient. One category of medical devices that can be inserted into a patient is catheters, which is a broad term, and could include several devices. One such catheter includes a drug delivery device using a hollow passage in the catheter to pump a drug to a selected location in the patient. Another catheter includes ablation technology where lasers are used to remove tissue. Another catheter includes an electrical contact that delivers an electrical signal to a point of interest inside a patient. While the above listed devices could all be considered catheters, the list is not exhaustive. Any of a number of other devices could be inserted inside a patient in such a way as to be classified as a catheter.
In this document, references to coordinates with respect to catheters will refer to axial locations and radial locations. Longitudinal or axial locations are locations along an insertion axis of a catheter. Radial locations will use the conventional 2-dimensional radial coordinates (r, θ) in a circle that is normal to the insertion axis. By combining an axial coordinate with the radial coordinates, a point can be located in three dimensional space relative to a given reference frame, such as the patient. Descriptions of the insertion axis in this document will generally refer to depth inside a patient along a line. It should be noted that although catheters are generally not inserted along a straight line, a generally linear depth model will be used for ease of discussion. Also, the axial end, or tip of the catheter that is inserted into a patient is referred to herein as the distal end of the catheter, while the axial end of the catheter that remains toward the outside the patient is referred to as the proximal end.
In one method of inserting a primary catheter, a secondary catheter is used to guide the primary catheter to the target location within the patient. In this configuration, the primary catheter is referred to as a micro-catheter, and the secondary catheter is referred to as a host catheter. Smaller catheters are desirably less invasive to the patient. In one type of surgical procedure, several micro-catheters are inserted in the same small opening in the patient at one time. However, the micro-catheters frequently lack the structural rigidity to be accurately inserted into the patient. The host catheter provides such rigidity. The micro-catheter and host catheter configuration is convenient because is allows more precise insertion of the more delicate micro-catheters.
A problem associated with the micro-catheter and host catheter configuration is that when several micro-catheters need to be inserted through a small incision, there is limited space available for insertion. The host catheter is typically of a large diameter that is similar in size to the diameter of the incision. There is not adequate room for several host catheters to each insert one micro-catheter.
One prior approach to this problem has been to insert multiple micro-catheters along a single host catheter. As shown in FIG. 1, a micro-catheter 150 can be inserted through one of multiple lumens 122 in a host catheter 100, and directed from a proximal end 120 of the host catheter 100 to various exiting openings 112 at a distal tip 110 of the host catheter 100. In this way, several micro-catheters can be inserted through an incision, thereby keeping the procedure less invasive. The example shown in FIG. 1 also allows a choice of several radial directions for the micro-catheter 150, depending on which lumen 122 of the host catheter 100 is chosen for insertion.
A limitation of this approach is that when using a single host catheter to implant multiple micro-catheters, all the micro-catheters must be implanted at the same depth inside the incision. Additionally, only one micro-catheter can be implanted in each radial direction, because each directional channel only accommodates one micro-catheter.
One approach to avoiding this limitation has been to further increase the number of channels in the host catheter, and to have the channels exit the host catheter at various depths and radial directions along the host catheter. In this way, by choosing an appropriate channel in the host catheter, each micro-catheter can be implanted at varying depths or radial orientations. However, this approach necessarily involves a larger, more invasive, host catheter, and the choices of depth locations and radial directions for the micro-catheters is limited by the predetermined exit locations of channels in the host catheter.
What is needed is a device and method to implant several micro-catheters at varying depths with a larger range of positioning options that does not require a larger, more invasive host catheter.
Another problem with the previous listed approaches occurs when using another type of procedure, where it is desirable to leave the micro-catheters implanted in the patient for extended periods of time, up to several days or weeks. A micro-catheter that is left implanted in a patient for extended periods of time is referred to as a “chronic” micro-catheter. In this type of procedure it is impractical to leave the host catheter inserted in the patient, because it is bulky, and extends a substantial distance outside the patient, and may be accidentally bumped over the extended time period. There is also an increased risk of infection with the larger opening being exposed for an extended time period. It is difficult or impossible to remove the host catheter of the previous examples and leave the micro-catheters implanted in their locations.
As further shown in FIG. 1, the distal tips of catheters, such as the distal tip 160 of micro-catheter 150, are small and typically have a diameter that is similar to a diameter along the axial length of the catheter. However, the proximal tips of catheters often have large fittings attached to them that are used for coupling to external, secondary medical devices. In FIG. 1, micro-catheter 150 is shown with a fitting 172 located at its proximal end 170. The fittings 172 are typically permanently attached to the micro-catheters 150. Micro-catheters are typically inserted into a close tolerance, enclosed longitudinal channel to guide them to the target location. The problem associated with removing the host catheter and leaving behind the micro-catheter is that the close tolerance, longitudinal channel will not fit over the much larger fitting 172 on the proximal tip of the micro-catheter. Because existing devices require axial removal of the host catheter, if the host catheter is to be removed, the micro-catheter must also be removed.
What is needed is a host catheter that can be removed while allowing the micro-catheter to remain implanted at its target location inside the patient.